Method Of Manufacturing A Workpiece With Multiple Metal Layers

ABSTRACT

A mold for making a workpiece is shown performing the steps of positioning a workpiece in a cavity of the mold, moving a first mold piece and a second mold piece towards a closed configuration with an extending wall of the first mold piece pressing into a peripheral portion of the workpiece so as to hold the workpiece between the first and second mold pieces, wherein a space is defined between the workpiece and a surface of the first mold piece in the closed configuration, the space receiving a molding material so as to form at least a second layer of the workpiece, and pressing the extending wall of the first mold piece into the peripheral portion of the workpiece to form a seal between the extending wall and the workpiece to prevent flow of a fluid through the seal. Moveable pieces for such a mold are shown.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is Continuation of U.S. patent application Ser. No.14/065,745, filed 29 Oct. 2013, now pending, which is a Division of U.S.patent application Ser. No. 13/747,833, filed 23 Jan. 2013, now pending,which was a continuation-in-part of U.S. patent application Ser. No.13/651,980 filed on 15 Oct. 2012, which is itself a continuation-in-partof U.S. patent application Ser. No. 13/277,673 filed on 20 Oct. 2011,which claims priority in Chinese Patent Application No. 2011 0037281.4,filed 1 Feb. 2011, the contents of these applications being incorporatedherein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a workpiece,such as a plate, with multiple metal layers. For the purpose of thisinvention, where the context allows, the terms “metal” and “metals”shall also include “alloys of metal” and “alloys of metals”respectively. It should also be understood that, for the purpose of thisinvention, the metal layers may be made of a same metal or differentmetals.

BACKGROUND OF THE INVENTION

With the rapid development in the communication, consumer electronic andcomputer industries (so called “3C industries”), consumers not onlyexpect good performance of such products (so called “3C products”) (suchas processing speed and storage capacity), but also a high class anddurable cosmetic surface of such products. A metal casing with goodstrength and light weight will thus become more and more important to 3Cproducts. Such characteristics have also become the consumerrequirements or expectation of products in other industries, such as thehousehold industry and automotive industry. In most products, there is aneed to over-mold at least one metal layer onto another metal layer, forexample to form a cover or a plate. There is therefore a need to improvethe joining or bonding strength between two metal layers, which hasbecome a significant production requirement.

A conventional colorful plastic casing of an electronic product iseasily broken and damaged by external impact, while a casing of a singlemetal layer may rust due to environmental factors, or subsequent surfacetreatment cannot be performed on the casing due to the limitation ofmaterial properties. Therefore, casings with multiple metal layers withthin thickness, good cosmetic performance, good strength for resistingexternal impact, and good corrosion resistance are needed to solve thevarious shortcomings of casings of a single metal layer. In the priorart, a casing for a consumer electronic apparatus which is formed ofdouble metal layers or of a mechanical laminate of materials is usuallyprepared by vacuum evaporation or ion sputtering, which entails highmanufacturing cost. However, as such a prior art casing is not good forreceiving surface treatment involving wet process, such as plating andanodizing, it is less corrosion resistant.

In conventional techniques, solid-state welding processes (such as coldwelding, friction welding and ultrasonic welding) may be used forbonding a veneer to a cast metal part. However, such solid-state weldingprocesses may significantly increase the complexity and cost of theprocessing flow. Therefore, persons skilled in the art are still lookingfor effective methods of manufacturing a workpiece with multiple metallayers which is less costly and less complex.

In addition, there is an ever-increasing requirement for electronicproducts (such as tablet computers and smart phones) and domesticelectrical appliances to be as compact and slim as possible. Consumersalso make the same requirements on products in the automotive industryand household product industry. Consumers are at the same time making ahigher and higher demand on the functions and capability of suchproducts. Manufacturers are thus looking for ways to make bodies of theproducts as compact as possible while retaining sufficient space forhousing the necessary components. Existing methods do not allow a thinlayer of metal to be injected onto and bonded/engaged with a layer ofmetal to form a workpiece with multiple metal layers. In addition, assuch products get compacter and slimmer, problems arise as regardspost-treatment, such as trimming and computer numerical control (CNC)works, which are required for achieving the necessary features.

As such products get more and more compact and slim, problems arise asregards post-treatment (such as trimming) of such workpieces as covers,housings, casings and chassis, because such post-treatment will exertpressure on the workpieces, which may deform the workpieces.

It is thus an object of the present invention to provide a method ofmanufacturing a workpiece with multiple metal layers, a mold and aworkpiece with multiple metal layers in which the aforesaid shortcomingsare mitigated or at least to provide a useful alternative to the tradeand public.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of manufacturing a workpiece with multiple metal layers, themethod including the steps of (a) providing a mold with at least arunner, a gate and a cavity, (b) providing in the cavity of the mold afirst metal layer made of a first metal, the first metal layer having asurface, the surface being roughened and/or including at least oneengagement structure, and (c) injecting a molten second metal onto thesurface of the first metal layer to form a second metal layer on thefirst metal layer wherein said second metal layer engages with saidroughened surface of said first metal layer or with said engagementstructure of said surface of said first metal layer, wherein said moltensecond metal enters said cavity of said mold at a speed of at leastsubstantially 70 meters per second (m/s).

According to a second aspect of the present invention, there is provideda mold including a first mold piece and a second mold piece, whereinsaid first mold piece and said second mold piece are movable relative toeach other between an open configuration in which said first mold pieceand said second mold piece are detached from each other and a closedconfiguration for holding a semi-finished workpiece between said firstmold piece and said second mold piece, and wherein at least said firstmold piece includes a wall member which, when said mold is in saidclosed configuration and holds a semi-finished workpiece, punches intoat least part of said semi-finished workpiece to form a seal betweensaid wall member and said semi-finished workpiece which prevents flow ofa fluid through said seal.

According to a third aspect of the present invention, there is provideda workpiece with multiple metal layers, said workpiece being formed byinjecting at least a second metal layer onto a first metal layer,wherein each of said first metal layer and second metal layer includesat least one engagement structure.

According to a fourth aspect of the present invention, there is provideda mold including a first mold piece and a second mold piece, whereinsaid first mold piece and said second mold piece are movable relative toeach other between an open configuration in which said first mold pieceand said second mold piece are detached from each other and a closedconfiguration in which said first mold piece and said mold piece areengaged with each other to form a cavity for containing a semi-finishedworkpiece, wherein said first mold piece includes a passageway allowingsupply of molding material into said cavity, and wherein said mold iswithout a channel allowing flow of molding material out of said cavity.

According to a fifth aspect of the present invention, there is provideda method of manufacturing a workpiece with multiple metal layers, saidmethod including steps (a) providing a first metal layer made of a firstmetal, (b) pre-treating said first metal layer, (c) placing saidpre-treated first metal layer in a mold, and (d) injecting a moltensecond metal onto said surface of said pre-treated first metal layer toform a second metal layer on said pre-treated first metal layer.

According to a sixth aspect of the present invention, there is provideda workpiece with multiple metal layers, said workpiece being formed byinjecting at least a second metal layer onto a first metal layer,wherein said second metal layer is of a thickness of not more thansubstantially 0.5 mm.

According to a seventh aspect of the present invention, there isprovided a method of manufacturing a workpiece with multiple metallayers, said method including steps (a) providing a mold with at least arunner, a gate and a cavity, (b) providing a first metal layer made of afirst metal, said first metal layer having a surface, said surfaceincluding at least one engagement structure, (c) pre-treating said firstmetal layer, (d) placing said pre-treated first metal layer in saidmold, and (e) injecting a molten second metal onto said surface of saidfirst pre-treated metal layer to form a second metal layer on saidpre-treated first metal layer, wherein said molten second metal enterssaid cavity of said mold at a speed of at least substantially 70 metersper second (m/s), wherein said second metal layer includes at least oneengagement structure which engages with said engagement structure ofsaid surface of said pre-treated first metal layer, wherein said moldincludes a first mold piece and a second mold piece, wherein said firstmold piece and said second mold piece are movable relative to each otherbetween an open configuration in which said first mold piece and saidsecond mold piece are detached from each other and a closedconfiguration in which said first mold piece and said second mold pieceare engaged with each other to form said cavity for containing saidpre-treated first metal layer, wherein said first mold piece includes apassageway allowing supply of said molten second metal, and wherein saidmold is without a channel allowing flow of said molten second metal outof said cavity.

According to an eighth aspect of the present invention, there isprovided a workpiece with multiple metal layers formed of a methodincluding steps (a) providing a mold with at least a runner, a gate anda cavity, (b) providing a first metal layer made of a first metal, saidfirst metal layer having a surface, said surface including at least oneengagement structure, (c) pre-treating said first metal layer, (d)placing said pre-treated first metal layer in said mold, and (e)injecting a molten second metal onto said surface of said firstpre-treated metal layer to form a second metal layer on said pre-treatedfirst metal layer, wherein said molten second metal enters said cavityof said mold at a speed of at least substantially 70 meters per second(m/s), wherein said second metal layer includes at least one engagementstructure which engages with said engagement structure of said surfaceof said pre-treated first metal layer, wherein said mold includes afirst mold piece and a second mold piece, wherein said first mold pieceand said second mold piece are movable relative to each other between anopen configuration in which said first mold piece and said second moldpiece are detached from each other and a closed configuration in whichsaid first mold piece and said second mold piece are engaged with eachother to form said cavity for containing said pre-treated first metallayer, wherein said first mold piece includes a passageway allowingsupply of said molten second metal, and wherein said mold is without achannel allowing flow of said molten second metal out of said cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of manufacturing a workpiece with multiplemetal layers according to an embodiment of the present invention;

FIG. 2-1 illustrates a device of manufacturing a workpiece with multiplemetal layers, for carrying out the method shown in FIG. 1, in which amold in the device is in an open configuration;

FIG. 2-2 illustrates the device shown in FIG. 2-1 in which the mold isin a closed configuration;

FIG. 2-3 is a partially enlarged view of the mold shown in FIG. 2-2;

FIG. 3 illustrates a method of manufacturing a workpiece with multiplemetal layers, according to a further embodiment of the presentinvention;

FIG. 4 illustrates a mold of manufacturing a workpiece with multiplemetal layers, for carrying out the method shown in FIG. 3;

FIG. 5 illustrates a method of manufacturing a workpiece with multiplemetal layers, according to a yet further embodiment of the presentinvention;

FIG. 6 illustrates a workpiece with multiple metal layers manufacturedby the method shown in FIG. 5;

FIG. 7 illustrates a method of manufacturing a workpiece with multiplemetal layers, according to a still further embodiment of the presentinvention;

FIG. 8 illustrates a first workpiece with multiple metal layersmanufactured by the method shown in FIG. 7;

FIG. 9A illustrates a second workpiece with multiple metal layersmanufactured by the method shown in FIG. 7;

FIG. 9B illustrates a third workpiece with multiple metal layersmanufactured by the method shown in FIG. 7;

FIG. 10A to 100 illustrate the process whereby a second metal in moltenform is injected into a mold to bond or engage with a first metal layer,in a method according to a further embodiment of the present invention;

FIG. 11 is a sectional view of an alternative mold suitable for use in amethod according to the present invention;

FIG. 12 is a partial sectional view of the first metal layer of FIG. 11after engagement with a second metal layer;

FIG. 13 is a side view of a first metal layer, after pre-treatment, andready for injection of a molten second metal, according to a stillfurther embodiment of the present invention;

FIG. 14A is a side view of a cover of multiple metal layers, includingthe first metal layer of FIG. 13;

FIG. 14B is a partial enlarged view of FIG. 14A; and

FIG. 15 is a top partial view of a cover of multiple metal layers with athin bay covered in part by a second metal layer.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a method of manufacturing a workpiece with multiplemetal layers according to an embodiment of the present invention.Generally speaking, in this method, a first metal layer in the form of asemi-finished plate formed of a first metal is disposed in a mold. Asecond metal (which is different from the first metal) in liquid(molten) form is then injected into the mold and onto the plate, so asto form a second metal layer on the first metal layer (S101). The secondmetal layer in the mold is then pressed by a pressure in the mold (S102)to facilitate bonding of the second metal layer to and with the firstmetal layer. It should of course be understood that a third metal (whichmay be the same as or different from the first and second metals) inliquid form may be injected onto the first metal layer or the secondmetal layer to form a workpiece with three metal layers by repeating theabove operation.

The injection operation includes different aspects, such ashigh-pressure and high speed injection molding, pouring and/or flowing.The pressure, the speed at which the second metal is injected into themold and the short time duration in which the second metal covers thefirst metal layer all assist in improving the adhesiveness and strengthof bonding between the first metal layer and the second metal layer,removing bubbles in the second metal when in liquid state, and improvingthe compactness of the second metal layer, so that only very few poresare left after cooling and curing of the second metal layer, therebyachieving the strength of a composite metal. Such may also prevent theformation of a liquid flow mark due to flowing of the second metal inliquid form during injection. Pressing the second metal layer may alsoenable a surplus of the second metal in liquid form to overflow.

FIG. 2-1 and FIG. 2-2 illustrate a device 201 for manufacturing aworkpiece with multiple metal layers, for carrying out the method shownin FIG. 1. The device 201 includes a mold 202 with a front mold 208 anda rear mold 207. The mold 202 is shown in FIG. 2-1 in an openconfiguration in which the front mold 208 and the rear mold 207 aredetached from each other. A semi-finished metal cover 203 (constitutinga first metal layer) formed of a first metal is disposed on the rearmold 207 of the mold 202. FIG. 2-2 shows the mold 202 in a closedconfiguration in which the semi-finished cover 203 is held between thefront mold 208 and the rear mold 207. When the mold 202 is in the closedconfiguration, a second metal in liquid form 2041 (which is a differentmetal from that of the first metal layer 203) is injected onto thesemi-finished cover 203 in the mold 202, so as to form a second metallayer 204 on the cover 203.

FIG. 2-3 is a partially enlarged view of FIG. 2-2, and shows that themold 202 includes a pressing component 205 for applying a pressure onthe second metal layer 204 in the mold 202.

In a further embodiment, a space is provided between the rear mold 207and the pressing component 205, so that the second metal in liquid form2041 may be injected into the space. Moreover, the mold 202 additionallyincludes an overflow port 206, so that a surplus of the second metal inliquid form 2041 overflows through the overflow port 206 when thepressing component 205 presses the second metal layer 204.

Although, in the foregoing discussions, it is mentioned that the firstmetal is different from the second metal, it is of course envisaged thatthe first metal layer and the second metal layer may be made of a samemetal.

In a yet further embodiment of the present invention, and as shown inFIG. 3, a method of manufacturing a workpiece with multiple metal layersincludes steps of injecting a first metal in liquid form into a spacebetween a rear mold and a first front mold in cooperation with eachother, so as to form a first metal layer on the rear mold (S301), andwhen the rear mold operates in cooperation with a second front mold andwhen the first metal layer on the rear mold is in a semi-solid moltenstate, injecting a second metal in liquid form onto the first metallayer so as to form a second metal layer on the first metal layer(S302). Again, the first metal layer and the second metal layer may bemade of the same or different metals.

The difference between the method shown in FIG. 3 and the method shownin FIG. 1 lies mainly in that, in the method shown in FIG. 3, the secondmetal in liquid form is injected onto the first metal layer and thesecond metal layer is formed when the first metal layer is still in asemi-solid molten state. This not only improves the adhesiveness betweenthe first metal layer and the second metal layer, but also reduces costand saves time, thereby improving the yield.

A device 401 for implementing the method shown in FIG. 3 is shown inFIG. 4. As shown in FIG. 4, the device 401 includes a first front mold402 which can operate in cooperation with a rear mold 407, and inject afirst metal in liquid form 4031 onto the rear mold 407, so as to form afirst metal layer 403 on the rear mold 407. The device 401 also includesa second front mold 408, which is co-operable with the rear mold 407 toinject a second metal in liquid form 4041 onto the first metal layer 403when the first metal layer 403 is still in a semi-solid molten state, soas to form a second metal layer 404 on the first metal layer 403.

When the second front mold 408 operates in cooperation with the rearmold 407, a space is provided between the rear mold 407 and a pressingcomponent 405, so that the second metal in liquid form 4041 may beinjected into the space.

Moreover, the pressing component 405 in the second front mold 408 may beused for applying a pressure on the second metal layer 404. Furthermore,the rear mold 407 further includes an overflow port 406, so that asurplus of the second metal in liquid form 4031 may overflow through theoverflow port 406 when the pressing component 405 applies a pressure onthe second metal layer 404.

The device 401 further includes a movement component, for relativelymoving the rear mold 407 between the first front mold 402 and the secondfront mold 408. For example, the rear mold 407 may be moved from thefirst front mold 402 to the second front mold 408 after the first metalin liquid form 4031 is injected; or the first front mold 402 is movedaway after the first metal in liquid form 4031 is injected, and thesecond front mold 408 is moved to a position operating in cooperationwith the rear mold 407, so as to inject the second metal in liquid form4041 onto the first metal layer 403. Through this arrangement, theinjection of both the first metal in liquid form 4031 and the secondmetal in liquid form 4041 is performed in the same device 401, thussimplifying the production process.

A workpiece with three or more metal layers may be formed by repeatingthe above steps.

Each of the first metal layer and the second metal layer may be formedof stainless steel, iron, zinc, aluminum, magnesium, chromium, titanium,copper, beryllium, nickel and alloy of these metals. A first metal layerwith a smaller specific weight may first be formed, and then a secondmetal layer with a larger specific weight is formed. Alternatively, afirst metal layer with a larger specific weight may first be formed, andthen a second metal layer with a smaller specific weight is formed. Forexample, if the first metal layer is formed of a zinc alloy, and thesecond metal layer is formed of an aluminum alloy, the strength of acomposite metal may be achieved, and subsequent anodizing surfacetreatment may be performed on the second metal (aluminum alloy) layer.In another example, the first metal layer is formed of an aluminum alloyor a magnesium alloy, and the second metal layer is formed of stainlesssteel, so that subsequent treatment such as direct currentelectroplating or vacuum evaporation may be conveniently performed on asurface of the second metal layer, thereby further forming a subsequentmetal or non-metal layer.

Not only does the workpiece with multiple metal layers manufacturedaccording to a method of the present invention have the strength andelasticity of a composite metal, but also subsequent surface treatment(such as heat treatment, anodizing surface treatment, Galvanic plating,vacuum coating/film treatment, coating treatment, painting treatment,and corrosion resistant treatment) may be performed on the metalworkpiece, as required, to further improve the adhesiveness between themetal layers and the strength and corrosion resistance of the workpiece,and to make the design of covers made of such workpieces more flexible.

A method of manufacturing a workpiece with multiple metal layers,according to a yet further embodiment of the present invention is shownin FIG. 5. The method shown in FIG. 5 includes steps of disposing asemi-finished metal workpiece (such as a plate formed of a first metallayer) in a mold, in which a surface of the semi-finished workpiece isroughened (S501). Subsequently, a second metal in liquid form isinjected onto the roughened surface of the semi-finished workpiece, soas to form a second metal layer on the semi-finished workpiece, in whichthe second metal in liquid form covers and fills the roughened surfaceof the semi-finished plate (S502). The roughened surface of thesemi-finished plate can be formed on either a cosmetic surface or aninner surface of the semi-finished plate. A third metal in liquid formmay be injected onto the second metal layer to form a three-layer metalplate by repeating the above operation.

FIG. 6 shows a plate with multiple metal layers manufactured by themethod shown in FIG. 5. As shown in FIG. 6, a semi-finished plate 612formed of a first metal is disposed in a mold 610. A surface 613 of thesemi-finished plate 612 is roughened. A second metal in liquid form isinjected onto the roughened surface 613 of the semi-finished plate 612,to form a second metal layer 614 on the semi-finished plate 612 whichsufficiently covers and fills the roughened surface 613 of thesemi-finished plate 612. Such an arrangement increases the adhesivestrength between the semi-finished plate 612 and the second metal layer614. The semi-finished plate 612 and the second metal layer 614 may bemade of the same metal or different metals. The roughened surface 613 ofthe semi-finished plate 612 may be formed of a plurality of recesses,holes, grooves, balls or protrusions or a combination of these. Theroughened surface 613 of the semi-finished plate 612 may be formedmechanically and/or chemically. By way of such an arrangement,detachment of the semi-finished plate 612 and the second metal layer 614from each other is at least hindered.

FIG. 7 shows a method according to a still further embodiment of thepresent invention. This method includes disposing a semi-finished plateformed of a first metal in a mold, in which a surface of thesemi-finished plate is provided with at least one engaging structure(S701), and injecting a second metal in liquid form onto the surface ofthe semi-finished plate, so as to form a second metal layer on thesemi-finished plate, in which the second metal in liquid form caps,fills and engages with the engaging structure on the surface of thesemi-finished plate (S702). The engaging structure of the semi-finishedplate can be formed on either a cosmetic surface or an inner surface ofthe semi-finished plate. A third metal in liquid form may be injectedonto the second metal layer to form a three-layer metal plate byrepeating the operation.

FIG. 8 illustrates a plate with multiple metal layers manufacturedaccording to the method shown in FIG. 7. As shown in FIG. 8, asemi-finished metal plate 812 formed of a first metal is disposed in amold 810. A surface of the semi-finished plate 812 is formed with atleast one engaging structure 813. The engaging structure 813 may be ahook, a buckle, a trench, a protrusion, a groove or a combination ofthese structures. A second metal in liquid form is injected onto thesurface of the semi-finished plate 812, to form a second metal layer 814on the semi-finished plate 812 which sufficiently caps, fills andengages with the engaging structure 813 on the surface of thesemi-finished plate 812. By way of such an arrangement, at least part ofthe second metal layer 814 is confined to a space defined by theengaging structure 813, so as to fix the semi-finished plate 812 withthe second metal layer 814. Such an arrangement at least hindersdetachment of the semi-finished plate 812 and the second metal layer 814from each other.

In molding, the molten molding material (such as a molten metal) isinjected from an injector nozzle of a molding machine to flow through asprue, then a runner, then a gate, through which the molten moldingmaterial enters the cavity of the mold. More particularly, a sprue is achannel allowing flow of the molten molding material from the injectornozzle towards the mold cavity. A runner is a channel in fluidcommunication with the sprue and guides the molten molding material toflow from the sprue towards the mold cavity. The runner is joined withthe gate and the gate acts as an entrance through which molten moldingmaterial in the runner enters the mold cavity.

To further enhance the strength of bonding/engagement between the firstmetal layer and second metal layer, in an embodiment of the presentinvention, the second metal in liquid form is injected from the injectornozzle at such a speed that the second metal in liquid form exits therunner and enters the cavity of the mold via the gate of the mold at aspeed of at least 70 meters per second (m/s). This speed will hereafterbe called the “ex-gate speed”. In one embodiment, to achieve an ex-gatespeed of 70 m/s, it is arranged such that the second metal in liquidform exits the sprue and enters the runner at a speed of at least 3.5m/s. This latter speed will hereafter be called the “ex-sprue speed”.

FIG. 9A illustrates a plate with multiple metal layers according to anembodiment of the present invention. A semi-finished plate 912 formed ofa first metal is first disposed in a mold 910. A surface 913 b of thesemi-finished plate 912 is roughened to form a plurality of recesses,holes, grooves, balls and/or protrusions, and at least one engagingstructure 913 a in the form of a hook, buckle, trench, protrusion and/orgroove is also formed on the surface 913 b. A second metal in liquidform is injected onto the roughened surface 913 b and the at least oneengaging structure 913 a of the semi-finished plate 912 at an ex-gatespeed of at least 70 m/s, to form a second metal layer 914 on thesemi-finished plate 912 which sufficiently covers and fills theroughened surface 913 b and engages the at least one engaging structure913 a of the semi-finished plate 912, so as to increase the joining andbonding or engagement strength between the semi-finished plate 912 andthe second metal layer 914 and to confine part of the second metal layer914 within a space defined by the engaging structure(s) 913 a.

FIG. 9B illustrates a plate with multiple metal layers according toanother embodiment of the present invention. A semi-finished plate 912′formed of a first metal is first disposed in a mold 910′. A surface ofthe semi-finished plate 912′ is formed with at least one engagingstructure 913 a′ in the form of a hook, a buckle, a trench, a protrusionand/or a groove. A second metal in liquid form is injected onto theengaging structure 913 a′ of the semi-finished plate 912′ at an ex-gatespeed of at least 70 m/s, to form a second metal layer 914′ on thesemi-finished plate 912′ which sufficiently covers, fills and engageswith the engaging structure 913 a′ of the semi-finished plate 912′. Suchan arrangement increases the joining and bonding or engagement strengthbetween the semi-finished plate 912′ and the second metal layer 914′ andconfines part of the second metal layer 914′ within a space defined bythe engaging structure(s) 913 a′. More particularly, bonding orengagement between the semi-finished plate 912′ and the second metallayer 914′ is enhanced because the inter-engagement and/or interlockingbetween the second metal layer 914′ and the engaging structure 913 a′hinders detachment of the semi-finished plate 912′ and the second metallayer 914′ from each other. More particularly, it can be said that eachof the semi-finished plate 912′ and the second metal layer 914′ has atleast one engagement structure which engage with each other.

The semi-finished plate (or the first metal layer) and the second metallayer may be made of the same metal or different metals, and the metalmay be stainless steel, iron, zinc, aluminum, magnesium, chromium,titanium, copper, beryllium, nickel or an alloy thereof.

The roughened surface of the semi-finished plate (i.e. first metallayer) in the above embodiments may be formed chemically and/ormechanically. For example, if the first metal layer is formed ofaluminum (Al), anodizing process may be used for forming pores on thesurface of first metal layer for joining with the molten second metal.In particular, the second metal in molten state may be trapped in thepores, so that the second metal will be fastened onto the first metallayer after cooling and curing thereof.

The plate may be used as a cover or an insert of an electronic device,or any other kinds of products/devices in other industries in which thedevices require better joining, bonding or engagement strength onmulti-metal construction.

The first metal layer and the second metal layer may be engaged togetherby bonding or confining a part of the second metal layer in a spacedefined by the engaging structure.

In above-mentioned methods, the second metal 614, 814, 914 and 914′ maybe injected onto the surface of the semi-finished plate (first metallayer) at an ex-gate speed of at least 70 m/s, and with an ex-spruespeed higher than 3 m/s, 3.5 m/s, 4.0 m/s, 4.5 m/s, 5.5 m/s, 6.0 m/s,6.5 m/s or above. In this way, the second metal layer can be of anextremely thin dimension, so that the recesses, holes, grooves, balls orprotrusions of the roughened surface and hook(s), buckle(s), trench(es),protrusion(s) or groove(s) of the engaging structure can be well capped(or covered) and filled by the second metal. In a preferred embodiment,the thickness of the second metal layer may be not more than 0.5 mm(such as 0.5 mm, 0.3 mm, 0.2 mm or 0.1 mm) by adjusting the ex-gatespeed (e.g. by adjusting the speed at which the second molten metal isejected from the injection nozzle), or depending on the 3D-design ofproduct, which may become important in future.

In view of the above, high speed of flow of the second molten metal is acritical parameter in minimizing the fall in temperature of the secondmolten metal during its flow from the injection nozzle to the moldcavity. Localized melting on the surfaces of the two metals which aregoing to be joined or bonded together can only result in a weak bonding.As such, post-processes (for examples, laser welding, resistance weldingand some other welding processes which are known in the market) areneeded to enhance the joining or bonding strength between the two metallayers. In the present invention, a bolted locking mechanism (or boltedlocking space) is provided on the first metal layer for guiding thesecond metal in molten form to be trapped by the designated spacedefined by the bolted locking mechanism, as the engaging structures 913a and 913 a′ depicted in FIGS. 9A-9B and discussed above.

In particular, a purpose of injecting the second metal in liquid forminto the mold at a high speed is to ensure that the second metal fillsup the cavity in a very short time, and thus the second metal is stillin the molten stage when it fills up the cavity of the mold to form thesecond metal layer. As shown in the example illustrated in FIGS. 10A to10C, the total time duration starting from that shown in FIG. 10A (whenthe molten second metal exits the sprue and enters the runner, at pointA), through that shown in FIG. 10B (when the molten second metal haspassed through the runner and is about to enter the gate, at point B),until that shown in FIG. 10C (when the molten second metal fills up thecavity of the mold, at point C) is not more than 0.02 s, with a totaldisplacement of 130 mm. Of this time duration of 0.02 s, the timeduration which the molten second metal takes to fill up the cavity onlyis not more than 0.005 s after it enters the cavity of the mold. In thisexample, the speed at which the molten second metal exits the sprue andenters the runner is 3.5 m/s, and the speed at which the molten secondmetal exits the gate and enters the cavity of the mold is 70 m/s.

To further enhance the engagement and bonding between the two metallayers, as shown in FIG. 11, a mold 1100 for manufacturing a plate withmultiple metal layers according to this invention has an upper mold 1102with a barrier in the form of an endless wall 1104 which extends awayfrom a surface of the upper mold 1102 directly facing a lower mold 1106.When the upper mold 1102 is in the configuration shown in FIG. 11, inwhich the upper mold 1102 is aligned with the lower mold 1106 and asemi-finished metal plate 1108 (being a first metal layer) ready forinjection of the second metal in molten form is held between the uppermold 1102 and the lower mold 1106, the wall 1104 contacts and is pressedto cut into the semi-finished plate 1108 to form a seal which preventsflow of a fluid (including a gas and a liquid) through the seal. The gasmay be air and the liquid may be a liquid molding material, such as thesecond metal in molten form. A space 1110 is also formed between theupper mold 1102 and the semi-finished plate 1108. The space 1110 is in afluid-communicable relationship with the injector nozzle via the sprue,runner and gate of the mold. The space 1110 reduces further oxidation ofthe molten second metal during its flow in the mold. Because of the highspeed at which the second metal in molten form exits the gate and entersthe cavity, and with the help of the space 1110 (which reduces furtheroxidation of the second metal in molten form), the molten second metalcan engage with and/or penetrate the roughened surface and/or theengagement element on the semi-finished plate 1108 in a very shortperiod of time, say of no more than 0.005 s, after it has entered thespace 1110, to thereby enhance the strength of engagement between thetwo layers of metal (meaning the semi-finished plate 1108 and the metallayer formed of the cooled-down second metal). On the other hand, in theabsence of the wall 1104 and, thus, the fluid-proof seal between thewall 1104 and the semi-finished plate 1108, due to the connection of theoutside atmosphere and the cavity through the traditional air ventingsystem, the molten second metal will further be further cooled down andoxidized during the injection process. The surface of the molten secondmetal will become oxidized and will be extended to the coming moltensecond metal. The surface tension of the oxidized molten second metaland/or semi-solid second metal will be higher, causing higher viscosityof the molten second metal, which will slow down the flow of the moltensecond metal. It will then be difficult for the molten second metal topenetrate or engage with the engagement elements of the semi-finishedplate 1108, in particular if such engagement elements are of a height ofless than 0.5 mm and a width of less than 0.5 mm, or engagement elementsof a depth of at least 0.5 mm.

Although the engagement elements may be of a height of at least 0.5 mm,the second metal layer may be of a lesser thickness. As shown in FIG.12, the semi-finished plate 1108 is schematically shown with twoengagement elements, each being a hook 1112, which are spaced apart fromeach other. The hooks 1112 extend from an upper surface 1114 of theplate 1108 by a height of 0.5 mm. A volume of molten second metal isinjected into the space between the hooks 1112 to form a second metallayer 1116 engaged with the plate 1108. Depending on the structural anddesign requirements, the thickness of the second metal layer 1116 may bemore than, equal to, or less than the height of the hooks 1112. Inparticular, in FIG. 12, the second metal layer 1116 is shown as being ofa thickness (e.g. 0.4 mm, 0.3 mm or less) which is less than the heightof the hooks 1112.

The mold 1100 includes a passageway through which molding materials(such as molten metals) may be supplied to the cavity of the mold whenthe mold 1100 is in the closed configuration. As distinct from existingpractice, however, there is no channel in the mold 1100 through whichexcess molding material (i.e. the molten metal) exits the cavity of themold 1100 to become burrs and flash, which have to be trimmed off afterthe molding process. On the other hand, when the mold 1100 is used, anyexcess molten second metal will flow over the first metal layer/plate1108 and will still form part of the product. It is thus not necessaryto carry out any trimming step after the method according to thisinvention, because there is no “over-flow material” to be trimmed off.

Although FIG. 11 shows the wall 1104 as being provided by the upper mold1102, it is envisaged that, depending on the designs of the products,the wall 1104 may be provided by the lower mold 1106, e.g. on a surfacefacing directly the upper mold 1102.

A method according to this invention possesses at least the followingadvantages:

-   (a) the molded product can be ejected after the injection process,    which is different from the ordinary casting process in which the    product has to be cooled down before it can be ejected from the    cavity,-   (b) the molten second metal covers the first metal layer when the    molten second metal is still in liquid form,-   (c) further oxidation of the molten second metal before it is cooled    down is reduced, thus allowing the molten second metal to fully    engage with or penetrate into different parts of the roughened    surface and/or engagement elements (such as grooves, pores,    recesses) of the semi-finished plate (being a first metal layer). It    provides the opportunity to form the interior features in net shape    and to reduce a lot of post-treatment processes and CNC works, thus    saving further cost,-   (d) as all the molten metal is trapped, with no overflow of such    metal, the edges around the first and second metal layers become    dense and sealed. There is thus no gap between the metal layers, in    particular between the boundaries or between the joining lines of    the metal layers, which is observable by end users, thus ensuring    cosmetic quality. In addition to being a cosmetic treatment for the    product, such also prevents liquid (such as water, DI water, acidic    solutions, alkaline solutions or the like) from seeping between the    metal layers. This at least reduces the potential problem of    galvanic corrosion of the product,-   (e) in cases where the workpiece is to form the outer casing of a    finished product, the surface which will form the outside surface of    the finished product will have no trace of the injected material,    thus presenting a more aesthetically pleasing outlook, and-   (f) as the second metal layer can be very thin (of not more than 0.5    mm), if a workpiece is to form a casing of a product, space of the    interior of the product is saved, thus allowing more freedom to the    designers.

In a further embodiment of the present invention, and as shown in FIGS.13 to 14B, a first metal layer (e.g. a semi-finished plate 1200) ispre-treated before molding. The plate 1200, which is made of a firstmetal, is originally of a generally rectangular cross-section. Thesemi-finished plate 1200 conforms generally with the shape and contour(in particular the outer contour) of the component which it is intendedto form. Some of the first metal is removed from the plate 1200 to formone or more recesses, e.g. thin bays 1202, on an upper surface 1204 ofthe plate 1200. These bays 1202 are of a depth d of 0.3 mm or less,while the thickness D of the first metal layer 1200 is around 0.8 mm.

The pre-treated semi-finished plate 1200 is then placed within thecavity of a mold. A molten second metal is then injected onto the uppersurface 1204 of the pre-treated plate 1200 to form a second metal layer1206, and to engage with the pre-treated plate 1200 to form a bi-layermetal workpiece. Some of the second metal is received within the bays1202 of the plate 1200, so as to engage the pre-treated plate 1200 withthe second metal layer 1206. It is of course possible to form aworkpiece with more layers of metal by repeating the above steps. Itshould be noted that the second metal layer 1206 may cover only part ofthe bays 1202.

In addition, and as shown in FIG. 14A, because of the high speed atwhich the molten second metal is injected onto the upper surface 1204 ofthe plate 1200, the second metal layer 1206 so formed by the secondmetal can form structures which extend away from a major surface of thesecond metal layer 1206 of the plate 1200. Such structures may be screwboss 1208 and other mechanical, structural components 1210.

It is found in practice that this arrangement of pre-treating thesemi-finished plate 1200 (in particular the removal of some of the firstmetal from the plate 1200 to form two recesses in the form of thin bays1202 on the upper surface 1204 of the plate 1200) before molding may beadvantageously combined with the use of mold 1100 with the endless wall1104 discussed above. With such a combined method, there will be no“waste material”, as any excess molten second metal (i.e. molten secondmetal beyond the minimum amount necessary for molding onto the firstmetal layer) will be kept within the mold 1100 to form at least part ofthe second metal layer 1206, which forms useful parts of the finalworkpiece/product.

An advantage associated with adopting such a combined method is that allexcess or surplus molten second metal (if any) will become part of thefinal workpiece/product in a planned manner, which could assist instrengthening the features formed by the second metal. In addition, asit is not necessary to post-treat any overflow material, the combinedmethod is both environmentally-friendly and cost-saving.

As mentioned above, the second metal layer 1206 may cover only part ofthe bays formed on the first metal layer. As shown in FIG. 15, a cover1302 formed of a first metal layer is formed with a shallow bay 1304along the periphery. Molten second metal is then molded on the firstmetal layer to form a second metal layer, in such a way that part of thebay 1304 is covered by the molten second metal. Hashed areas 1306 shownin FIG. 15 are areas of the thin 1304 not covered by the molten secondmetal. During the molding process, the bay 1304 receives the moldingmaterial (i.e. molten second metal) and performs air-venting functionfor leaking air generated during the molding process.

The present invention seeks to at least mitigate the shortcomingsassociated with the prior art, and to manufacture a workpiece withmultiple metal layers at a lower cost and with a higher yield, bypreparing materials according to actual material consumption, thus beingmore environmentally friendly and cost efficient than the technologycurrently available. Meanwhile, different metals of double layers ormultiple layers may be designed to completely or partially cover asubstrate, so as to meet the requirements for appearance and mechanicalperformance at the same time, which will save a large amount of work indeveloping different alloy materials and save global resources.

The method of the present invention achieves good adhesiveness betweenmultiple metal layers and improves the metal compactness and the surfacesmoothness, and facilitates subsequent metal surface treatment.

It should also be understood that, for the purpose of this invention, a“workpiece with multiple metal layers” does not mean that the workpieceis formed exclusively of metal(s). It is envisaged that a “workpiecewith multiple metal layers” may be formed additionally of othermaterials, e.g. plastics material. As an example, such a workpiece maybe formed of two metal layers which are bonded/engaged with each otheras discussed above and a plastic layer which is bonded/engaged with oneof the two metal layers. There is thus no limitation on the number oflayers of materials involved or the number of materials involved, solong as the workpiece includes two metal layers which are bonded/engagedwith each other as discussed above.

Although the technical contents and features of the present inventionare described above, various variations and modifications can be made bypersons of ordinary skill in the art without departing from the teachingand disclosure of the present invention. Therefore, the scope of thepresent invention is not limited to the disclosed embodiments, butencompasses other variations and modifications that do not depart fromthe present invention as defined by the appended claims.

1. A method of manufacturing a workpiece made from at least two layerscomprising the steps of: (a) providing a mold including a first moldpiece and a second mold piece which are movable relative to each otherbetween an open configuration in which the first mold piece and thesecond mold piece are detached from each other and a closedconfiguration, the first mold piece and the second mold pieces adaptedto define a mold cavity therebetween, a semi-finished workpiececomprising at least one layer of the workpiece disposable within themold cavity and having a peripheral portion, the peripheral portion heldbetween the first mold piece and the second mold piece when in theclosed configuration, at least the first mold piece including a wallextending from a surface thereof facing a surface of the second moldpiece and configured for engaging the peripheral portion of thesemi-finished workpiece disposed therebetween, (b) positioning thesemi-finished workpiece in the mold cavity defined between the firstmold piece and the second mold piece, (c) moving the first mold pieceand the second mold piece relative to each other towards the closedconfiguration, the extending wall pressing into the peripheral portionfor holding the semi-finished workpiece between the first and secondmold pieces, a space defined between the semi-finished workpiece and thesurface of the first mold piece when the mold pieces are in the closedconfiguration, the space adapted for receiving a molding materialtherein for forming at least a second layer of the semi-finishedworkpiece, and (d) pressing the extending wall of the first mold pieceinto the peripheral portion of the semi-finished workpiece for forming aseal between the extending wall and the semi-finished workpiece toprevent a flow of fluid through the seal.
 2. The method according toclaim 1 wherein the extending wall is endless.
 3. The method accordingto claim 1, further comprising a step (e) of, after the mold pieces arein the closed configuration and the space is formed between thesemi-finished workpiece and the first mold piece, supplying the moldingmaterial to the space for forming the at least second layer of theworkpiece.
 4. The method according to claim 3, further comprising a step(f) of applying pressure to the molding material at a location separatefrom where the molding material is supplied into the space, the pressurepromoting bonding of the molding material to the semi-finishedworkpiece.
 5. The method according to claim 1, further including apassage that, when the mold is in the closed configuration, allowssupply of the molding material into the space.
 6. The method accordingto claim 5, wherein the space is in fluid-communicable relation with aninjector via the passage for supplying a flow of the molding materialinto the space.
 7. The method according to claim 6, wherein the passagecomprises a sprue, a runner and a gate of the mold and wherein theinjector and the passage provide the flow of molding material from thegate at a speed of at least seventy meters per second and covers theworkpiece in no more than five milliseconds.
 8. The method of claim 6,wherein the injector and the passage provide the flow of moldingmaterial into the space at a speed of at least seventy meters persecond.
 9. The method of claim 8, wherein the workpiece comprises aroughened surface, an engagement structure, or both, and the flow ofmolding material covers the workpiece in no more than five milliseconds.10. A mold comprising a first mold piece means and a second mold piecemeans, wherein the first mold piece means and the second mold piecemeans are movable relative to each other between an open configurationin which the first mold piece means and the second mold piece means aredetached from each other and a closed configuration for holding aworkpiece between the first mold piece means and the second mold piecemeans, and wherein at least the first mold piece means comprises a wallmeans which, when the mold is in the closed configuration and holds aworkpiece, presses into at least part of the workpiece to form a sealbetween the wall means and the workpiece which prevents flow of a fluidthrough the seal.
 11. The mold according to claim 10, wherein the wallmeans is endless.
 12. The mold according to claim 10, further includinga passage that, when the mold is in the closed configuration and a spaceis formed between the workpiece and the first mold piece means, allowsliquid molding material to flow into the space.
 13. The mold accordingto claim 12, wherein the space is in fluid-communicable relation with aninjector means via a means for passage of the liquid molding materialinto the space.
 14. The mold of claim 13, wherein the injector means andthe means for passage provide the flow of liquid molding material at aspeed of at least seventy meters per second.
 15. The mold of claim 14,wherein the workpiece comprises a roughened surface, an engagementstructure, or both, and the flow of liquid molding material covers theworkpiece in no more than five milliseconds.
 16. The mold of claim 13,wherein the flow of liquid molding material covers the workpiece in nomore than five milliseconds.
 17. A mold for manufacturing a workpiecemade from at least two layers comprising: a first mold piece means and asecond mold piece means which are movable relative to each other betweenan open configuration in which the first mold piece means and the secondmold piece means are detached from each other and a closedconfiguration; the first mold piece means and the second mold piecespiece means adapted to define a mold cavity therebetween when in theclosed configuration; the cavity configured to receive a semi-finishedworkpiece comprising a first layer within the mold cavity, thesemi-finished workpiece having a peripheral portion, the first moldpiece means and the second mold piece means adapted to hold theperipheral portion therebetween when in the closed configuration, atleast the first mold piece means including a wall means extending from asurface thereof facing a surface of the second mold piece means andconfigured for engaging the peripheral portion of the semi-finishedworkpiece disposed therebetween; the extending wall means pressing intothe peripheral portion for holding the semi-finished workpiece betweenthe first mold piece means and the second mold pieces piece means, aspace defined between the semi-finished workpiece and the surface of thefirst mold piece means when the first mold piece means and the secondmold piece means pieces are in the closed configuration, the spaceadapted for receiving a molding material therein for forming at least asecond layer of the workpiece; the extending wall means of the firstmold piece mean pressed into the peripheral portion of the semi-finishedworkpiece to form a seal between the extending wall means and thesemi-finished workpiece which prevents flow of a fluid through the seal.18. The mold according to claim 17, wherein the space is influid-communicable relation with an injector means via a means forpassage of a flow of the molding material into the space at a speed ofat least seventy meters per second.
 19. The mold of claim 18, whereinthe first layer comprises a roughened surface, an engagement structure,or both, wherein the flow of molding material covers the workpiece in nomore than five milliseconds.
 20. The mold of claim 17, wherein the spaceis in fluid-communicable relation with an injector means via a means forpassage of a flow of the molding material into the space, wherein theflow of molding material covers the workpiece in no more than fivemilliseconds.